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A three-dimensional covalent organic framework (COF-505) constructed from helical organic threads, designed to be mutually weaving at regular intervals, has been synthesized by imine condensation reactions of aldehyde functionalized copper(I)-bisphenanthroline tetrafluoroborate, Cu(PDB)2(BF4), and benzidine (BZ).The copper centers are topologically independent of the weaving within the COF structure and serve as templates for bringing the threads into a woven pattern rather than the more commonly observed parallel arrangement. The copper(I) ions can be reversibly removed and added without loss of the COF structure, for which a tenfold increase in elasticity accompanies its demetalation. The threads in COF-505 have many degrees of freedom for enormous deviations to take place between them, throughout the material, without undoing the weaving of the overall structure. [ABSTRACT FROM AUTHOR]

Capturing CO2 from humid flue gases and atmosphere with porous materials remains costly because prior dehydration of the gases is required. A large number of microporous materials with physical adsorption capacity have been developed as CO2-capturing materials. However, most of them suffer from CO2 sorption capacity reduction or structure decomposition that is caused by co-adsorbed H2O when exposed to humid flue gases and atmosphere. We report a highly stable microporous coppersilicate. It has H2O-specific and CO2-specific adsorption sites but does not have H2O/CO2-sharing sites. Therefore, it readily adsorbs both H2O and CO2 from the humid flue gases and atmosphere, but the adsorbing H2O does not interfere with the adsorption of CO2. It is also highly stable after adsorption of H2O and CO2 because it was synthesized hydrothermally. [ABSTRACT FROM AUTHOR]

Heterogeneous palladium catalysts, which are supported on ordered mesoporous silica-carbon nanocomposites, have been applied in water-mediated coupling reactions of chlorobenzene without assistance of any phase-transfer catalysts. Characterization by XRD, TEM, N2 sorption, FT-IR, TG, XPS, and H2 chemisorption techniques reveals the highly ordered mesostructure, high surface areas (~345 m2/ g), large pore volumes (~0.46 cm3/g), uniform mesopore sizes (~6.3 nm), hybrid silicate and carbonaceous compositions, and a high dispersion of palladium nanoparticles (about 3 nm) in the mesopores. The catalyst exhibits a high yield for trans-stilbene (~60%) in the Heck coupling reaction of chlorobenzene and styrene at 100 °C and for biphenyl (46%) in the Ullmann coupling reaction of chlorobenzene at 30 °C, using water as a solvent. When substituted aryl chlorides (hydroxyl, methoxyl, and methyl) are involved in the Ullmann reaction, the yields of symmetrical substituted biphenyl are also higher than 44% (this value reaches 86% for the coupling reaction of 4-chiorophenol) at a low temperature of 30 °C. This heterogeneous catalyst is stable, which shows negligible metal leaching, and can be reused more than 20 times. For comparison, the catalytic activities for Pd catalysts supported on pure mesoporous polymeric, carbonaceous, and silicate frameworks are also investigated. The results clearly indicate that the pore wall nature shows great influence on the dispersion of metallic Pd species and, in turn, the catalytic performance. [ABSTRACT FROM AUTHOR]

A novel self-assembly route to ordered silica—organic hybrids using well-defined siloxane oligomers with alkoxy functionality and covalently attached alkyl chains has been investigated. Various hybrid mesostructures were obtained by hydrolysis and polycondensation without the use of any structure- directing agents. The oligomers 1(Cn), having an alkylsilane core and three branched trimethoxysilyl groups, formed highly ordered lamellar phases when n = 14-18, while those with shorter alkyl chains formed cylindrical assemblies, slightly distorted two-dimensional (2D) hexagonal structures (n = 6-10), and a novel 2D monoclinic structure (n = 12). Furthermore, the mixtures of 1(Cn) with different chain lengths yielded well-ordered 2D hexagonal phases, possibly due to the better packing of the precursors. The hybrids consisting of cylindrical assemblies were converted to ordered porous silica with tunable pore sizes upon calcination to remove organic groups. The liquid-state 29Si NMR analysis of the hydrolysis and polycon-densation processes of 1(Cn) revealed a unique intramolecular reaction yielding primarily the oligomer with a tetrasiloxane ring which is a new class of amphiphilic molecule having both self-assembling ability and high cross-linking ability. We also found that the mesostructure (lamellar or 2D hexagonal) was strictly controlled by varying the number of siloxane units per alkyl chain. These results provide a deeper understanding of the present self-assembly process that is strongly governed by the molecular packing of oligosiloxane precursors. [ABSTRACT FROM AUTHOR]

Two kinds of highly ordered mesoporous silica materials (FDU-1 1, FDU-1 3) with novel three- dimensional (3-D) tetragonal and orthorhombic structures were synthesized by using tetra-headgroup rigid bolaform quaternary ammonium surfactant [(CH3)3NCH2CH2CH2N(CH3)2CH2(OHCH2)11OC6H4C6H4O(CH2)11- CH2N(CH3)2CH2CH2CH2N(CH3)2·4Br1 (C3-12-12-3) as a template under alkaline conditions. High-resolution transmission electron microscopy (HRTEM), small-angle X-ray scattering (SAXS), and X-ray diffraction (XRD) show that mesoporous silica FDU-1 1 has primitive tetragonal P4/mmm structure with cell parameters a = b = 8.46 nm, c = 5.22 nm, and c/a ratio = 0.617. N2 sorption isotherms show that calcined FDU-11 has a high BET surface area of ∼1490 m²/g, a uniform pore size of &sim2;.72 nm, and a pore volume of ∼1 .88 cm³/g. Mesoporous silica FDU-13 has primitive orthorhombic Pmmrn structure. The cell parameters are a = 9.81, b = 5.67, and c = 3.66 nm. N2 sorption isotherms show that calcined FDU-13 has a high BET surface area of 1210 m²/g, a uniform mesopore size of ∼1.76 nm, and a large pore volume of ∼1.83 cm³/g. Such low symmetries for 3-D mesostructures (tetragonal and orthorhombic system) have not been observed before even in amphiphilic liquid crystals, which maybe resulted from an oblate aggregation of the bolaform surfactant and its strong electrostatic interaction with inorganic precursor. A probable mechanism has been proposed for the formation of such a 3-D low symmetrical mesostructure. These results will further extend the synthesis of mesoporous materials and may open up new opportunities for their new applications in catalysis, separation, and nanoscience. [ABSTRACT FROM AUTHOR]

Since the discovery of AIPO-n molecular sieves at the beginning of the 1980s,' open-framework metallophosphates have attracted considerable attention not only because of their rich compositional and structural diversity but also because of their potential applications in catalysis, separation, as well as in environmental and advanced functional materials. Soon after the discovery of carbon nanotubes in 1991, one- dimensional (1D) nano structured materials sparked worldwide interest because of their unique electronic, optical, and mechanical properties.